Revert "Go a little faster by comparing against undefined"

This reverts commit 82251a3.
ce0f7ce0221b05879fa7c833f53216cd23176b5d
commit ce0f7ce0221b05879fa7c833f53216cd23176b5d
diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
@@ -1358,7 +1358,7 @@ export function createOrReusePrinter(o: ReusablePrinterOptions = {}) {
         + keyNum(o.target)
         + keyNum(o.newLine);
     let printer = printerCache.get(key);
-    if (printer === undefined) {
+    if (!printer) {
         printerCache.set(key, printer = createPrinter(o));
     }
     return printer;